The present invention relates to a high frequency power amplifier and a technology effective for application to a wireless communication apparatus such as a cellular phone or the like with the high frequency power amplifier built therein, and particularly to a technology for speeding up an open-loop type high frequency power amplifier capable of controlling a power supply voltage for output power FETs constituting the high frequency power amplifier to thereby control output power and improving efficiency thereof at a low output.
An output section on the transmitting side of a wireless communication apparatus (mobile communication apparatus) such as a mobile phone, a cellular phone or the like has built therein a module (called an “RF power module”) in which a high frequency power amplifier (generally provided in a multistage configuration) using semiconductor amplifying elements such as MOSFETs (field effect transistors), a GaAs-MESFET, etc. and its bias circuit are integrated into one.
Meanwhile, a cellular phone generally has a system configured in such a manner as to change an output (transmission power) so as to adapt to an ambient environment according to power level designation information sent from a base station in accordance with a use environment to thereby start a call and in such a way as not to cause interference between the cellular phone and other cellular phones.
An RF power module of a transmission-side output stage of a portable phone of a cellular type or system such as a North American Standard System of a 900 MHz band, an European GSM (Global System for Mobile Communication) system or the like is provided with an APC (Automatic Power Control) circuit which effects feedback on a gate bias circuit for generating a gate bias voltage of each output power element so as to detect a DC level of an output and provide output power necessary for a call (e.g., Unexamined Patent Publication No. 2000-151310). Such a control system is generally called a “closed-loop type or system”.